As a system configuration of gas treatment equipment including a freezing compressor, a closed cycle system has heretofore been known which operates while circulating refrigerant gas. In a closed cycle system disclosed, for example, in the following Patent Literature 1 <in particular, see FIG. 1 of the following Patent Literature 1>, an expander is placed downstream of a compressor, and refrigerant gas discharged from a refrigerant gas outlet of the expander is returned to a refrigerant gas inlet of the compressor, and thus is recirculated. Accordingly, the closed system is always in a state in which the pressure at the refrigerant gas outlet of the expander is higher than the pressure at the refrigerant gas inlet of the compressor, and never operates in a state in which the pressure at the refrigerant gas outlet of the expander is lower than the pressure at the refrigerant gas inlet of the compressor.